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(#) Registered class is not instantiatable

!!! ERROR: Registered class is not instantiatable
   This is an error, and is also enforced at build time when
   supported by the build system. For Android this means it will
   run during release builds.

Id
:   `Instantiatable`
Summary
:   Registered class is not instantiatable
Severity
:   Fatal
Category
:   Correctness
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   Initial
Affects
:   Manifest files and resource files
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/MissingClassDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/MissingClassDetectorTest.kt)
Copyright Year
:   2012

Activities, services, broadcast receivers etc. registered in the
manifest file (or for custom views, in a layout file) must be
"instantiatable" by the system, which means that the class must be
public, it must have an empty public constructor, and if it's an inner
class, it must be a static inner class.

If you use a custom `AppComponentFactory` to instantiate app components
yourself, consider disabling this Lint issue in order to avoid false
positives.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
res/menu/my_menu.xml:13:Error: NotView must extend android.view.View
[Instantiatable]
    android:actionViewClass="test.pkg.NotView" /&gt;
                             ----------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here are the relevant source files:

`res/menu/my_menu.xml`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~xml linenumbers
&lt;menu xmlns:android="http://schemas.android.com/apk/res/android"&gt;
    &lt;item
        android:id="@+id/locale_search_menu"
        android:title="@string/locale_search_menu"
        android:icon="@*android:drawable/ic_search_api_material"
        android:showAsAction="always|collapseActionView"
        android:actionViewClass="test.pkg.SearchView" /&gt;
    &lt;item
        android:id="@+id/locale_search_menu"
        android:title="@string/locale_search_menu"
        android:icon="@*android:drawable/ic_search_api_material"
        android:showAsAction="always|collapseActionView"
        android:actionViewClass="test.pkg.NotView" /&gt;
&lt;/menu&gt;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`src/test/pkg/SearchView.kt`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers
package test.pkg
import android.widget.TextView
abstract class SearchView : TextView(null)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`src/test/pkg/NotView.kt`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers
package test.pkg
abstract class NotView : android.app.Fragment()
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/MissingClassDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `MissingClassDetector.testMenu`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Adding the suppression attribute `tools:ignore="Instantiatable"` on
  the problematic XML element (or one of its enclosing elements). You
  may also need to add the following namespace declaration on the root
  element in the XML file if it's not already there:
  `xmlns:tools="http://schemas.android.com/tools"`.

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="Instantiatable" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'Instantiatable'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore Instantiatable ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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